This project aims to establish the oncogenic mechanisms activated by ETV6 mutations in T- cell acute lymphoblastic leukemia (T-ALL). Our central hypothesis is that ETV6 mutations found in T- ALL result in expression of dominant negative ETV6 isoforms whose expression disrupts specific transcriptional regulatory networks that control cell proliferation, differentiation and survival in T-cell progenitor cells. In additin, we propose that ETV6 mutations cooperate with activating mutations in loss of function mutations and deletions in EZH2 in T-ALL. Thus, the goals of this research proposal are to define the transcriptional programs and oncogenic pathways responsible for the pathogenesis of mutant ETV6 induced T-ALL. To achieve these objectives we propose: (i) to define the transcriptional program controlled by mutant ETV6 in T-ALL; and (iii) to analyze the genetics of mutant ETV6 induced transformation using a mouse models of mutant ETV6 induced T-ALL.